select
    c_custkey,
    c_name,
    sum(l_extendedprice * (1 - l_discount)) as revenue,
    c_acctbal,
    n_name,
    c_address,
    c_phone,
    c_comment
from
    customer,
    orders,
    lineitem,
    nation
where
        c_custkey = o_custkey
  and l_orderkey = o_orderkey
  and o_orderdate >= date '1994-05-01'
  and o_orderdate < date '1994-08-01'
  and l_returnflag = 'R'
  and c_nationkey = n_nationkey
group by
    c_custkey,
    c_name,
    c_acctbal,
    c_phone,
    n_name,
    c_address,
    c_comment
order by
    revenue desc limit 20;
